reproduce (this is a W=1 build):
        # https://github.com/paulmckrcu/linux/commit/31c00ec5301cf02af354d57007bf0d79d5aef1c5
        git remote add paulmckrcu https://github.com/paulmckrcu/linux
        git fetch --no-tags paulmckrcu dev
        git checkout 31c00ec5301cf02af354d57007bf0d79d5aef1c5
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash kernel/rcu/